1. Field of the Invention
The present disclosure relates to solenoid valves, each of which is mounted in a fuel vapor treating system for controlling an amount of the fuel vapor flowing in the fuel vapor treating system.
2. Description of the Related Art
A gas vehicle is equipped with a fuel vapor treating system for preventing fuel vapor vaporized in a fuel tank from flowing into the atmosphere. The fuel vapor treating system includes a canister filled with an adsorbent and temporally trapping the fuel vapor by adsorbing the fuel vapor onto the adsorbent. The fuel vapor treating system has valves, each of which is generally composed of a solenoid valve, for opening and closing pipes communicating the fuel tank, the canister and the atmosphere each other in order to control flow of the fuel vapor in the fuel vapor treating system.
Japanese Laid-Open Patent Publication No. 2005-291241 discloses a solenoid valve having a first valve member, a second valve member, a second valve seat for the second valve member, an electromagnetic driving member, a first pathway and a second pathway for receiving and discharging fluid therethrough. The second valve member has a first valve seat for the first valve member and defines a communicating pathway for communicating the first pathway and the second pathway. When the first valve member and the second valve member contact the first valve seat and the second valve seat, respectively, communication between the first pathway and the second pathway is blocked. When the electromagnetic driving member moves the first valve member away from the first valve seat while the second valve member is contacting the second valve seat, the first pathway and the second pathway are communicated with each other via the communicating pathway. In this state, when differential pressure between the first pathway and the second pathway decreases, the second valve member moves away from the second valve seat due to biasing force from a spring, which biases the second valve member. As a result, a valve-opening area for flowing the fuel vapor increases, and thus the flow rate of the fuel vapor flowing from the first pathway into the second pathway also increases.
There has been a need for improved solenoids capable of controlling flow rate of fluid.